Although semiconductor light emitting diodes and laser diodes (both generally referred to herein as LEDs) occupy a growing share of the general lighting market, their adoption may be hindered by differences in their performance compared to the light sources they replace. For example, users, especially in the home lighting sector, are accustomed to and like to experience the dimming behavior of incandescent light bulbs, which both dim and shift in color to a lower color temperature “warmer” white as electric power to the light bulb is decreased. This behavior is not only typical of incandescent (typically tungsten filament) light bulbs, but is linked to radiation laws of physics and hence may be thought of as natural dimming. Reducing the temperature of the glowing filament in a light bulb by throttling the current passing through it not only changes light output, but also changes the spectrum of light emitted. The color temperature is decreased. LEDs and phosphor-converted LEDs generally do not behave in this manner.
Attempts to produce LED light sources with user-desired natural incandescent-like-dimming (ILD) behavior have involved, for example, designing that behavior into LED lamps or luminaires by using red-emitting, LEDs in combination with white LEDs. The red LEDs are powered up as the total power from the lamp or luminaire is ramped down, to red-shift the light output as it dims. These devices typically require at least three electrical contacts to their drive electronics. This approach adds complexity and cost to the drive electronics. Similarly, early attempts to achieve ILD behavior in fluorescent and compact fluorescent lamps also typically required complex driving circuitry.